The CrSi film is an important resistant material in the field of integrated circuits, owing to its high sheet resistance and low temperature coefficient of resistance. The preparation of CrSi film is compatible with the manufacture process of the semiconductor industry. With the high gauge factors, the CrSi film resistor has become an extensively applied component in the thin film strain gauge sensors.
The preparation of electronic integrated circuitry involves etching as a necessary processing step. In the etching procedure, a variety of etchants may be used according to the purposes and conditions of the etching.
Two major recipes for the etching of a CrSi film are the etchant with the major agent of HNO.sub.3 and that using H.sub.2 SO.sub.4 as its major agent. In the HNO.sub.3 group, the HNO.sub.3 /HF/H.sub.3 PO.sub.4 etchant and the HNO.sub.3 /HF/CH.sub.3 COOH/H.sub.2 O etchant are two good examples.
Owing to the presence of HNO.sub.3 in the HNO.sub.3 group etchants, the positive photoresist may lose its adhesion to the CrSi film during the heated etching procedure. As a result, formation of the outer edge of the pattern is subject to attack by the etchant. A worse scenario is that the photoresist may be separated from the CrSi film, causing distortion of the pattern.
Furthermore, owing to the strong oxidation characteristic of HNO.sub.3, the CrSi film surface exposed to the etchant would be passivated. The etching would therefore be retarded or cease.
On the other hand, in the H.sub.2 SO.sub.4 group, the H.sub.2 SO.sub.4 /H.sub.2 O and the H.sub.2 SO.sub.4 /HF/CH.sub.3 COOH/H.sub.2 O etchant are of extensive application in the industry. The H.sub.2 SO.sub.4 content of the etchant is most likely to react with the photoresist, especially the positive photoresist. The photoresist will then be burned which can subsequently lead to poor pattern definition and leave a deleterious residue.
As to the other etchants applicable to the CrSi film, there is an etchant containing 3 to 6 parts of HF and 4 to 6 parts of H.sub.2 O. This etchant contains a high HF content which hinders the integrity of the underlying Si-based films, such as SiO.sub.2.
The AlCl.sub.3 /H.sub.3 PO.sub.4 /H.sub.2 O is also a well-known etchant for the CrSi film. This etchant is not appropriate for mass production because the CrSi film pre-treatment with Zn-Pulver prior to the etching will reduce the productivity of the etching. Furthermore, the molybdaenmasken must be applied while using this etchant. This will raise the cost of the preparation of the film.